1. Field of the Invention
The present invention relates to an electric actuator provided with a ball spline shaft which is movable back and forth from an actuator body to the outside, driven by a rotary driving source.
2. Description of the Related Art
Electric actuators have been used, for example, in order to transport workpieces or position workpieces. Such an electric actuator is provided with a motor, a ball screw shaft which is linearly and substantially coaxially connected with a drive shaft of the motor by a coupling member, and a slider which is displaceable in the axial direction by a nut member externally fitted to the ball screw shaft.
In this arrangement, the motor is driven and rotated, and the rotary driving force thereof is transmitted to the ball screw shaft. Accordingly, the slider is displaced by the nut member which is screw-engaged with the ball screw shaft.
However, in the conventional electric actuator, the drive shaft of the motor and the ball screw shaft are connected linearly and substantially coaxially by the coupling member. Therefore, the axial size of the electric actuator is obtained by adding the length of the ball screw shaft and the length of the drive shaft of the motor. Thus, it is impossible to reduce a size of the electric actuator in the axial direction.
In order to shorten the electric actuator in the axial direction, the drive shaft of the motor and the ball screw shaft are arranged substantially in parallel to one another while they are separated from each other by a predetermined distance. A gear mechanism having a plurality of gears is interposed between the drive shaft of the motor and the ball screw shaft to transmit the rotary driving force.
However, when the rotary driving force of the motor is transmitted to the ball screw shaft in this structure, it is necessary to establish the concentricity for the gear and the nut member which are formed as separate members and which are coaxially connected to one another. Therefore, the centering alignment operation is complicated.